<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div id="app">
      <div>我今年 <input type="text" v-model.number="num" />岁</div>
      <div>五年后，你<input type="text" v-model="lastNum" />岁</div>
    </div>
    <script src="./vue.js"></script>
    <script>
      new Vue({
        el: '#app',
        data: {
          num: 20
        },
        computed: {
          lastNum: {
            get () {
              return this.num + 5
            },
            set (value) {
              this.num = value - 5
            }
          }
        }
      })
    </script>
  </body>
</html>
